34,495 research outputs found
How bio-friendly is the universe
The oft-repeated claim that life is written into the laws of nature are
examined and criticized. Arguments are given in favour of life spreading
between near-neighbour planets in rocky impact ejecta (transpermia), but
against panspermia, leading to the conclusion that if life is indeed found to
be widespread in the universe, some form of life principle or biological
determinism must be at work in the process of biogenesis. Criteria for what
would constitute a credible life principle are elucidated. I argue that the key
property of life is its information content, and speculate that the emergence
of the requisite information-processing machinery might require quantum
information theory for a satisfactory explanation. Some clues about how
decoherence might be evaded are discussed. The implications of some of these
ideas for fine tuning are discussed.Comment: 11 page conference report, no figure
Quantum mechanics and the equivalence principle
A quantum particle moving in a gravitational field may penetrate the
classically forbidden region of the gravitational potential. This raises the
question of whether the time of flight of a quantum particle in a gravitational
field might deviate systematically from that of a classical particle due to
tunnelling delay, representing a violation of the weak equivalence principle. I
investigate this using a model quantum clock to measure the time of flight of a
quantum particle in a uniform gravitational field, and show that a violation of
the equivalence principle does not occur when the measurement is made far from
the turning point of the classical trajectory. I conclude with some remarks
about the strong equivalence principle in quantum mechanics.Comment: 10 pages, 1 figure, research pape
Quantum fluctuations and life
There have been many claims that quantum mechanics plays a key role in the
origin and/or operation of biological organisms, beyond merely providing the
basis for the shapes and sizes of biological molecules and their chemical
affinities. These range from the suggestion by Schrodinger that quantum
fluctuations produce mutations, to the conjecture by Hameroff and Penrose that
quantum coherence in microtubules is linked to consciousness. I review some of
these claims in this paper, and discuss the serious problem of decoherence. I
advance some further conjectures about quantum information processing in
bio-systems. Some possible experiments are suggested.Comment: 10 pages, no figures, conference pape
Dry matter yields and quality of organic lupin/cereal mixtures for wholecrop forage
In view of climate change predictions and the general desirability of increasing the amount of home grown protein, a case exists for the investigation of lupins and lupin/cereal bicrop combinations as wholecrop forage on organic farms. A replicated randomised block trial is described which took place at the Royal Agricultural College, Cirencester, in 2005. This involved spring sown blue, white and yellow lupins, millet, wheat and triticale and lupin/cereal bi-crops. Data for dry matter yields for wholecrop silage, crude protein, MAD fi bre content and estimated ME, are presented for a single harvest. It is concluded that white lupins and white lupin bi-crops with spring wheat or triticale offer the best prospects for a viable wholecrop forage crop in an organic situation
The Energy-Momentum Tensor in Fulling-Rindler Vacuum
The energy density in Fulling-Rindler vacuum, which is known to be negative
"everywhere" is shown to be positive and singular on the horizons in such a
fashion as to guarantee the positivity of the total energy. The mechanism of
compensation is displayed in detail.Comment: 9 pages, ULB-TH-15/9
Quantum Determinism from Quantum General Covariance
The requirement of general covariance of quantum field theory (QFT) naturally
leads to quantization based on the manifestly covariant De Donder-Weyl
formalism. To recover the standard noncovariant formalism without violating
covariance, fields need to depend on time in a specific deterministic manner.
This deterministic evolution of quantum fields is recognized as a covariant
version of the Bohmian hidden-variable interpretation of QFT.Comment: 6 pages, revised, new references, Honorable Mention of the Gravity
Research Foundation 2006 Essay Competition, version to appear in Int. J. Mod.
Phys.
Does life's rapid appearance imply a Martian origin?
The hypothesis that the rapid appearance of life on Earth justifies the
belief that life is widespread in the universe has been investigated
statistically by Lineweaver and Davis. However, a rapid appearance could also
be interpreted as evidence for a nonterrestrial origin. I attempt to quantify
the relative probabilities for a nonindigenous versus an indigenous origin of
life on Earth, on the assumption that biogenesis involved one or more highly
improbable steps, using a generalization of the well known observer selection
argument of Carter. The analysis is specifically applied to a Martian origin of
life, with subsequent transfer to Earth within impact ejecta.Comment: 10 pages, no figures, research pape
Black hole versus cosmological horizon entropy
The generalized second law of thermodynamics states that entropy always
increases when all event horizons are attributed with an entropy proportional
to their area. We test the generalized second law by investigating the change
in entropy when dust, radiation and black holes cross a cosmological event
horizon. We generalize for flat, open and closed Friedmann-Robertson-Walker
universes by using numerical calculations to determine the cosmological horizon
evolution. In most cases the loss of entropy from within the cosmological
horizon is more than balanced by an increase in cosmological event horizon
entropy, maintaining the validity of the generalized second law of
thermodynamics. However, an intriguing set of open universe models show an
apparent entropy decrease when black holes disappear over the cosmological
event horizon. We anticipate that this apparent violation of the generalized
second law will disappear when solutions are available for black holes embedded
in arbitrary backgrounds.Comment: 14 pages, including 6 figures, to appear in Classical and Quantum
Gravity, reference adde
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